The first covid vaccine was granted regulatory approval in December 2020 by the UK medicines regulator Medicines and Healthcare products Regulatory Agency (MHRA).
Since then, more vaccines have been given approval and to date almost four million have had their booster jag alone.
But when booking the vaccine, many of us plan it out carefully so that if we do have a reaction - such as sore muscles and a fever - our day won't be ruined and we won't have to take time off of work as a result.
And because of this, one question that is asked a lot when it comes to the vaccine is 'why did I have a reaction but they didn't' and in a bid to answer that question, one NHS doctor took to TikTok to explain the reasoning
Dr Karan Ranj, an NHS surgeon and social media educator, explained: "If you had a strong reaction after getting the vaccine, does that mean a stronger immunity. If you had no side effects does that mean the vaccine didn't work?
"When you get a vaccine your immune system responds in two ways. The first is called the innate immune response. This is the cause of post-shot side effects like aches and pains.
"The second way your immune system responds is the adaptive immune response and that's the thing which helps your body get long-term immunity.
"So whether or not you had a reaction doesn't matter. It's all about that second response which doesn't have symptoms."
According to the NHS, most side effects are mild and should not last longer than a week, such as:
- A sore arm from the injection
- Feeling tired
- A headache
- Feeling achy
- Feeling or being sick
They state: "You may also get a high temperature or feel hot or shivery one or two days after your vaccination. You can take painkillers such as paracetamol if you need to. If your symptoms get worse or you're worried, call 111.
"If you have a high temperature that lasts longer than 2 days, a new, continuous cough or a loss or change to your sense of smell or taste, you may have covid. Stay at home and get a test.
"You cannot catch covid from the vaccine, but you may have caught it just before or after your vaccination."
